Allen,(posted 8690 days ago)Why do you rule out a light leak? This would also show up as plus density. How much added density would depend on the severity of the light leak.
But, I do have a few more questions: Does the are of added density only show up at one location on the film? The next time you process a roll, remove it from the reel very slowly. Note where each problem area is in relation to the reel. Do the problems overlap each time around the reel? Are they staggered around the reel? Do they show up on 35mm film? Can you process a test roll in a small tank with hand agitation?
This problem is very solvable. You need to test each variable before assuming that it is not the problem.
Let us know what you find.